1. Field of the Invention
This invention relates to a radar device and, specifically, to a radar device mounted on a vehicle and for detecting the positions of preceding vehicles and oncoming vehicles as viewed from the vehicle.
2. Description of Related Art
As a device for detecting objects by using a radar device, an object detector for correctly detecting objects has been reported (e.g., see patent document 1). As shown in FIG. 1, an object detector unit 140 in a conventional object detector 110 includes a grouping means 141 for grouping a plurality of detection point data corresponding to an object from a plurality of detection point data, a partial searching means 142 for searching and detecting a predetermined portion of the object to be detected from an image portion corresponding to the detection point data grouped by the grouping means, a straight line calculation means 143 for calculating two straight lines extending from the object detector unit 140 up to both ends of a portion detected by the partial searching means 142, and a detection point extraction means 144 for extracting, as detection point data corresponding to a portion of the object to be detected, the detection point data on the insides of the two straight lines calculated by the straight line calculation means 143 out of the detection point data grouped by the grouping means 141. The object detector unit 140 also includes an end point estimating means 145 and a state estimating means 146. The conventional object detector 110 also includes a camera 120 and a laser radar 130, and the conventional object detector 110 is connected with a braking unit 150.
The above constitution makes it possible to correctly detect objects by using the radar.
As technologies for a radar, an ACC (Adaptive Cruise Control System) and a CMBS (Collision Mitigation Brake System) have also been known. ACC makes it possible to travel (hereinafter referred to as “preceding vehicle”) ahead of a vehicle that has the ACC. The CMBS makes it possible to prevent a collision by automatically applying the brakes if the distance becomes short with respect to the preceding vehicle. The ACC and the CMBS must correctly grasp the positions of the preceding vehicles. A vehicle is usually provided with side mirrors, and electromagnetic waves transmitted from the radar device toward the preceding vehicle are reflected not only by the rear of the preceding vehicle but also by the side mirrors. Therefore, the objects detected based on the waves reflected by the side mirrors are recognized as objects different from the preceding vehicle which is equipped with side mirrors. Namely, a single preceding vehicle forms a plurality of objects, and capacity of a memory often becomes insufficient to store the data of the objects. In order to solve this problem, a “mirror judgment processing” has been developed.
The “mirror judgment processing” is a process for determining objects detected based on the waves reflected by side mirrors as objects that are based on a preceding vehicle equipped with the side mirrors. According to the mirror judgment processing, a predetermined range is set with the positions of the detected objects of the preceding vehicle as references, the objects detected within the range are assumed to be based on the preceding vehicle, and the data of only one object are representatively processed.
The mirror judgment processing will now be concretely described with reference to FIG. 2 which is a view looking down the lanes on where the vehicles are traveling. A vehicle 100 equipped with a radar device 10 is traveling on a lane 300 located on a left side of a halfway line 600 heading in the direction of arrow “a”. On the lane 300 it is presumed that a first preceding vehicle 101 is traveling heading in the direction of arrow “b” which is the same direction as arrow “a” ahead of the vehicle 100. Electromagnetic waves emitted from the radar device 10 toward the first preceding vehicle 101 are reflected by the rear of the first preceding vehicle 101. Therefore, the position of an object To that is detected becomes the rear of the first preceding vehicle 101.
It is presumed that the first preceding vehicle 101 is provided with mirrors (side mirrors) on both sides of the vehicle body. Electromagnetic waves emitted from the radar device 10 are reflected by the mirrors. The intensity of the electromagnetic waves reflected by the mirrors is high enough to detect objects T1 and T2. If the data of the detected objects T1 and T2 are stored together with the data of the object T0 of the first preceding vehicle 101, then the data of the three objects must be stored for one preceding vehicle. The maximum number of objects that the radar device is capable of storing is about 10, and it is not desired to store three objects per a vehicle. Therefore, in the mirror judgment processing, the objects T1 and T2 detected by being reflected by the mirrors are regarded to be based on the first preceding vehicle 101, and the data of the object T0 of the first preceding vehicle 101 are representatively processed.
In the mirror judgment processing as shown in FIG. 2, objects are regarded to be the same as the object T0 if they are detected in a predetermined range with the position of the object T0 of the first preceding vehicle 101 as a reference, e.g., if they are detected in a range A1 of ±dx0 in the transverse direction and dy0 in the longitudinal direction as viewed from the vehicle 100 with the position of the object T0 as a reference. For instance, the width 2dx0 in the transverse direction is 2.5 [m]. Hereinafter, the predetermined range which is regarded to be the same as the preceding vehicle is referred to as “preceding vehicle judging range”. Upon setting the preceding vehicle judging range in a range inclusive of the mirrors of the vehicle, the objects based on the reflection by the mirrors of the preceding vehicle can be regarded to be the same as the preceding vehicle, and the number of the data to be processed by the radar device can be brought into conformity with the number of the preceding vehicles.
The conventional mirror judgment processing is used for detecting a preceding vehicle traveling in the same direction as the present vehicle equipped with the radar device. On the other hand, in order to avoid collision of the present vehicle with other vehicles which approaches to the present, it is important to correctly detect the positions of the vehicles (hereinafter referred to as “oncoming vehicles”). In particular, the oncoming vehicles rapidly approaching the present vehicle and, therefore, it is desired to correctly detect the position of the oncoming vehicles within a short period of time. If the conventional mirror judging processing is used for detecting the oncoming vehicles, however, there remains a problem in that the positions of the oncoming vehicles cannot be correctly detected as described below.
Referring to FIG. 2, it is presumed that a first oncoming vehicle 201 and a second oncoming vehicle 202 are traveling on an opposite lane 400 in the directions of arrow c1 and c2 which are opposite to the direction in which the present vehicle 100 is traveling, and the positions of the detected objects are Tf1 and Tf2. If the mirror judgment processing is executed for the oncoming vehicles by setting the preceding vehicle judging range which is of the same size as the preceding vehicle, the objects can be regarded to be the same as the reference object Tf1 if they are detected in a range A1′ of ±dx0 in the transverse direction and dy0 in the longitudinal direction with the position of the object Tf, as a reference. If a distance (transverse positional difference) dx between Tf1 and Tf2 in the transverse direction is smaller than dx0 and if a distance (longitudinal positional difference) dy in the longitudinal direction is smaller than dy0, however, the position of Tf2 is included in the range A1′—Therefore, the second oncoming vehicle 202 is judged to be the same as the first oncoming vehicle 201 by the mirror judgment processing, and the position of the second oncoming vehicle 202 can no longer be grasped. This results in a delay in starting operation for avoiding the collision when the second oncoming vehicle 202 approaches the present vehicle 100.
As described above, if the conventional mirror judgment processing is used for detecting the oncoming vehicles, a problem occurs, i.e., the positions of the oncoming vehicles are not correctly detected.    [Patent document 1] JP-A-2010-32429